Recently, a mobile communication system in which a mobile terminal such as a portable phone and a base station device communicate with each other with radio has been widely used. The base station has a cell, which is a range within which the base station may communicate with mobile terminals. In a case where the mobile terminal moves from the cell of the base station with which the mobile terminal is communicating to the cell of another base station, handover from the base station involved in the current communication to another base station is conducted. The mobile terminal periodically searches for cells in proximity to the cell to which the mobile terminal belongs (cell search). The mobile terminal communicates with the base station that has a cell having a good reception level on the basis of the results of the cell search.
There is known an art of changing the period of the cell search on the basis of determining whether the mobile terminal remains in the current cell (see Patent Document 1). There is known another art of shortening the period of the cell search in such a manner that the base station stores information about a spread signal and a phase corresponding to the base station beforehand (see Patent Document 2). There is known a further art of notifying the mobile terminal of results of past learning about failure of handoff by the base station and performing the cell search based on the results of the past learning (see Patent Document 3).    Patent Document 1: Japanese Laid-Open Patent Publication No. 2003-348001    Patent Document 2: Japanese Laid-Open Patent Publication No. 2001-285909    Patent Document 3: Japanese Laid-Open Patent Publication No. 2000-287256